Solid state light-sources, such as light-emitting diodes (LEDs), are increasingly used as illumination devices for a wide variety of lighting and signaling applications. Light-emitting diodes have an extremely high brightness. Hence, the installation of LEDs in various general lighting applications typically requires the reduction of the brightness by many orders of magnitude. Especially in office environments the maximum luminance is preferably less than 2×104 cd/m2 to ensure a high visual comfort. A traditional approach to lower the brightness is to use a light scattering surface diffuser or volume diffuser at a respectable distance from the LED array. This option is effective for a number of applications where the volume of the optics is not critical.
Several attempts have been made to meet the requirements for optical distribution and uniformity. For instance, EP 2 390 557 A, discloses a luminaire having a curved, prismatic sheet. The curved, prismatic sheet is further provided with a plurality of elongated linear prism structures and an exit window. In this manner, there is provided a luminaire in which a respectable part of the light escapes directly from the LED through the exit window to outside so as to provide a specific intensity profile.
Despite the activity in the field, there remains a need for an improved light-emitting module which meets the requirement for uniformity, whilst a balance is kept between the flexibility of the light-emitting module and the size and number of components making up the light-emitting module.